The quality of fruit juice, in particular juice of citrus fruits, varies depending on the kinds of the plants, growing district, harvest, picking time, storage time and method, juicing time, etc. It has hence been difficult to provide a stabilized good flavor by the mere clarification treatment for removing pulp. One method which is currently being conducted for stabilizing the quality of citrus fruit juice is to selectively remove bitter components from the fruit juice. One known technique for carrying out the above method is to bring fruit juice into contact with an adsorbent to adsorb and separate bitter components only. Examples of such bitter components include naringin, which is a representative flavonoid compound. Although limonin, which is a terpenoid compound characteristic of citrus fruits, and the like are also known as other bitter components, the content thereof is very low. Consequently, the main purpose of bitterness removal is to remove naringin. In order for this compound, having a molecular weight of about 500, to be selectively and efficiently removed with an adsorbent, it is necessary to precisely design the hydrophobicity, i.e., chemical structure, and the pore structure of the adsorbent before the adsorbent is synthesized.
An example of bitterness removal with an adsorbent is described in, e.g., Journal of Food Industry Society of Japan, Vol 26, No. 1 (1979), pp. 1-5, in which an adsorbent comprising a styrene-divinylbenzene copolymer is used. However, the adsorbent shown in the above reference is not an adsorbent designed and synthesized for bitter-component removal. This prior art adsorbent has a specific surface area of about 700 m.sup.2 per g of the dry adsorbent and is unsatisfactory in treating ability. In JP-A-60-153780 (corresponding to U.S. Pat. No. 4,439,458) (the term "JP-A" as used herein means an "unexamined published Japanese patent application") is disclosed a method of bitter-component removal using a styrene-divinylbenzene copolymer. The adsorbent used in this prior art technique also has a specific surface area of from 500 to 700 m.sup.2 per g of the dry adsorbent. Further, JP-W-2-503516 (corresponding to U.S. Pat. No. 4,965,083) (the term "JP-W" as used herein means an "unexamined published International patent application based on a Japanese patent application") discloses a method in which a resin produced by post-crosslinking a similar styrene-divinylbenzene copolymer and then incorporating ionexchange groups thereinto to hydrophilize the crosslinked copolymer is used. This prior art resin is disadvantageous in that the process for producing the resin is complicated and involves many steps. In addition, the above resin has drawbacks in practical use in that handling thereof is troublesome, for example, because the resin should be treated with a chemical, e.g., an acid or alkali, before or after use for bitter-component removal since the resin contains ion-exchange groups.